Roberts Stephen P, Harrison Jon F, Dudley Robert
Department of Biological Sciences, University of Nevada, Las Vegas, 4505 S. Maryland Parkway, Las Vegas, NV 89154-4004, USA.
J Exp Biol. 2004 Feb;207(Pt 6):993-1004. doi: 10.1242/jeb.00850.
We assessed the energetic and aerodynamic limits of hovering flight in the carpenter bee Xylocopa varipuncta. Using normoxic, variable-density mixtures of O(2), N(2) and He, we were able to elicit maximal hovering performance and aerodynamic failure in the majority of bees sampled. Bees were not isometric regarding thorax mass and wing area, both of which were disproportionately lower in heavier individuals. The minimal gas density necessary for hovering (MGD) increased with body mass and decreased with relative thoracic muscle mass. Only the four bees in our sample with the highest body mass-specific thorax masses were able to hover in pure heliox. Wingbeat frequency and stroke amplitude during maximal hovering were significantly greater than in normodense hovering, increased significantly with body mass during normodense hovering but were mass independent during maximal hovering. Reserve capacity for wingbeat frequency and stroke amplitude decreased significantly with increasing body mass, although reserve capacity in stroke amplitude (10-30%) exceeded that of wingbeat frequency (0-8%). Stroke plane angle during normodense hovering was significantly greater than during maximal hovering, whereas body angle was significantly greater during maximal hovering than during normodense hovering. Power production during normodense hovering was significantly less than during maximal hovering. Metabolic rates were significantly greater during maximal hovering than during normodense hovering and were inversely related to body mass during maximal and normodense hovering. Metabolic reserve capacity averaged 34% and was independent of body mass. Muscle efficiencies were slightly higher during normodense hovering. The allometry of power production, power reserve capacity and muscle efficiency were dependent on the assumed coefficient of drag (C(D)), with significant allometries most often at lower values of C(D). Larger bees operate near the envelope of maximal performance even in normodense hovering due to smaller body mass-specific flight muscles and limited reserve capacities for kinematics and power production.
我们评估了木匠蜂（Xylocopa varipuncta）悬停飞行的能量和空气动力学极限。通过使用常氧、可变密度的氧气（O₂）、氮气（N₂）和氦气（He）混合物，我们能够在大多数采样的蜜蜂中引发最大悬停性能和空气动力学失效。蜜蜂的胸部质量和翅膀面积并非呈等比例关系，在较重的个体中，这两者都不成比例地更低。悬停所需的最小气体密度（MGD）随体重增加而增加，随相对胸部肌肉质量减少而降低。在我们的样本中，只有四只具有最高体重特异性胸部质量的蜜蜂能够在纯氦氧混合气中悬停。最大悬停时的翅膀拍动频率和冲程幅度显著大于常密度悬停时，在常密度悬停时随体重显著增加，但在最大悬停时与体重无关。翅膀拍动频率和冲程幅度的储备能力随体重增加而显著降低，尽管冲程幅度的储备能力（10 - 30%）超过了翅膀拍动频率的储备能力（0 - 8%）。常密度悬停时的冲程平面角度显著大于最大悬停时，而最大悬停时的身体角度显著大于常密度悬停时。常密度悬停时的功率产生显著小于最大悬停时。最大悬停时的代谢率显著高于常密度悬停时，并且在最大悬停和常密度悬停时均与体重呈负相关。代谢储备能力平均为34%，且与体重无关。常密度悬停时肌肉效率略高。功率产生、功率储备能力和肌肉效率的异速生长取决于假定的阻力系数（C(D)），在较低的C(D)值时，显著的异速生长最为常见。由于体重特异性飞行肌肉较小以及运动学和功率产生的储备能力有限，较大的蜜蜂即使在常密度悬停时也接近最大性能的极限。
